The present invention relates to a communication network system for connecting a plurality of networks, and more particularly to an internetworking apparatus referred to as a router which connects a plurality of networks at network layer levels, and an internetworking apparatus referred to as a router which has a router function of connecting a plurality of networks at network layer levels as well as a bridging function of connecting a plurality of networks at data link layer levels.
As for an apparatus for connecting a plurality of networks, there are known a bridge which performs cross connection in a data link layer (especially, a media access sub-layer) of a network system hierarchy, and a router which performs the cross connection in a network layer as a layer having a rank higher than that of the bridge, or the like.
The bridge manages an MAC (Media Access Control) address, and judges whether or not a reception frame from a certain network (being also referred to as "reception packet data") is forwarded to other networks on the basis of the contents of the destination MAC address in the reception frame and a filtering address table as forwarding control information.
Moreover, in the router as well, on the basis of the internetworking address in the reception frame and an address resolution table in the router, a predetermined route or an optimal route is selected to perform the forwarding processing of the reception frame.
Incidentally, there are some kinds of protocol used in the network layer. As a typical example, there is well known an IP (Internet Protocol). In this IP protocol, an IP address is used as the internetworking address. Then, the MAC address of the adjacent route corresponding to the destination IP address is written in the address resolution table.
Further, in recent years, an apparatus which has the router function as well as the bridging function has been developed to be used for the connection between the different kind networks. This apparatus is called a router. This router performs the routing with respect to the frame data amenable to the protocol which is supported by the apparatus of interest, i.e., able to be subjected to the routing, out of the various protocols used in the network layer, thereby to perform the across connection in the network layer. On the other hand, this router performs the forwarding processing of the frame data in the media access sub-layer, i.e., the bridging processing with respect to the frame data amenable to the protocol which is not supported by the apparatus of interest, i.e., cannot be subjected to the routing.
As described above, the network apparatus, such as the bridging apparatus, the router and the router, is designed in such a way as to have at least two or more communication ports, and the processor for performing the above forwarding processing called the routing or bridging.
As the prior art example having such a configuration, the general operation of the router will hereinbelow be further described in detail. The packet data which has been received from a certain communication port is stored in a buffer memory, and then the packet data is subjected to the routing processing by the processor, whereby the router obtains a network to which the data will be transmitted. Then, by sending the packet data from another communication port corresponding to the destination network, the router performs the routing of the packet data.
FIG. 2 is a diagram showing schematically a plurality of networks which are connected to one another through routers. In the figure, eight networks are connected to one another through five routers. Paying attention to a router A out of those routers, networks A, B, C and D are connected to ports a, b, c and d of the router A, respectively. Now, if the data is intended to be sent from a terminal A1 in the network A to a terminal G2 in a network G connected to a router E, the packet data addressed from the terminal A1 to the terminal G2 is transmitted with the physical destination address as an address for the port a of the router A. After receiving this packet data, the router A forwards the packet data to one of the networks B, C and D, i.e., performing the routing processing. In order to perform this routing processing, the router A needs to know previously which of the networks B, C and D must the packet data addressed to the terminal G2 be forwarded to. In this example, on the assumption that the packet data must be transmitted to the network B, i.e., the router B, the packet data is transmitted with the physical destination address as an address for the port e of the router B. The same routing is also performed in the routers B and E, and thus finally, that packet data reaches the terminal G2.
As for the prior art for performing such a routing processing at high speed, there is given the technology disclosed in JP-A-62-181551. According to this technology, a buffer memory for storing the packet data received from one port, and a buffer memory for storing the packet data received from the other port are provided separately and independently of each other, and the management of the buffer memorys is performed with the hardware.
Moreover, as for the prior art for performing the packet transmission between ports at high speed, there is given the technology disclosed in an article "OUTLINE OF TCP/IP AND INTERNET" p.17 issued on Dec. 19, 1990 by Net One Systems Co. Ltd. According to this technology, a high speed bus is provided for the high speed port transmission.
In the above prior art technology, the following points will become problems.
Although the transmission of the packet data can be performed at high speed in the router according to the prior art, the means for performing the routing is provided only in one place. Therefore, the routing provides a limit, and thus there is a limit to the number of ports capable of being supported and the communication traffic. Accordingly, it is difficult to smoothly extend the organization of the port menue and the like of the router from a small scale to a large scale and improve the performance in correspondence to the port traffic or the number of ports.
Further, in recent years, there has been increased the necessity of the dynamic routing to recognize the configuration and the like of the network during the operation of the network to dynamically produce, add, change and delete the forward information for the routing processing (in the above prior art example, the information for the forwarding which is assumed to be previously known by each router). That is, there is required the processing of a routing protocol (e.g., RIP (Routing Information Protocol), OSPF (open Shortest Path First) and the like in the TCP/IP protocol group) for exchanging the information about the network between the routers. Further, the means for performing the routing in the prior art must also perform the processing of a network management protocol (e.g., SNMP (Simple Network Management Protocol) and the like in the TCP/IP protocol group) for communicating the management information such as performance information of the router itself to the management master station on the network. Therefore, the original forwarding performance cannot show sufficiently. Accordingly, it is difficult for the prior art router to cope with an FDDI (Fiber Distributed Data Interface) as a high speed LAN (Local Area Network) of 100 Mbps (Mega bit per second) which has been developed in recent years, and a high speed line of 155 Mbps such as a broad-band ISDN (hereinafter, referred to as B-ISDN for short, when applicable) which is expected to come into wide use in the future and an ATM (Asyncronized Transfer Mode) as one form thereof.